The
Doctor pointed at Bernice. 'The wench's mind is addled,' he said. 'Arrest her
before she spreads her ungodly heresy.'

The TARDIS
is caught in the gravitational field of a dark star. The Doctor and Bernice are
forced to evacuate, and find themselves stranded in medieval France - a brutal
time of crusades and wars of succession.

As the
Albigensian crusade draws to its bloody conclusion, men inflict savage
brutalities on each other in the name of religion. And the TARDIS crew find
their lives intertwined with warring Templars, crusaders and heretics. While
The Doctor begins a murder investigation in a besieged fortress, Bernice finds
herself drawn to an embittered mercenary who has made the heretics' fight his
own. And they both realize that to leave history unchanged they may have to
sacrifice far more than their lives.